2000 Audi A6 Questions

Yesterday in a warm climate the engine quit while exiting a freeway. Help pushing it off to the side, EPC indicator came on. After a cool down (was not overheating) the engine started and drove about .5 miles and stalled again. Waited about 1 hr. and started drove about 1 mile, stalled and called AAA to have it towed. EPC stayed on. Got home and started right up but have not driven it.

I want to buy a 2000 Audi A6 has 89,000 miles that is smoking thru the muffler. The guy says he took it to Audi Service and they said that the bank 1 turbo needs to be replaced. How hard of a fix is it and can I just replace the bad one with a used one from the junk yard?